Problem with monitorSystemUpdate in another languages

Hi, we have problem with encoding of function shell_exec called in /usr/local/ispconfig/server/bil/classes/monitor_tools.inc.php on line 900. This function updating database with result of shell_exec('apt-get -s -q dist-upgrade'). But in (for example) czech, this function returns result with bad encoding and monitor of updates doesn't work. It returns something like 'a:1:{s:6:"output";s:3604:"&Auml;'. It's uncomplete and unable to unserialize. There are few possible ways how to fix that, but I think, that the best is call with this function shell_exec('apt-get -s -qq dist-upgrade'). In this result is enough informations. What do you mean?